class_docstr: Gym Dictionary with arbitrary keys updatable after instantiation
  
  Example:
     space = FlexDict({})
     space['key'] = spaces.Box(4,)
  See also: documentation for gym.spaces.Dict
code: def assertSpace(self, space):
      err = "Values of the dict should be instances of gym.Space"
      assert issubclass(type(space), gym.spaces.Space), err
  
file_path: ray/rllib/utils/spaces/flexdict.py
imports: import gymnasium
  from ray.rllib.utils.annotations import PublicAPI
label_desc: Use image node_id 2 for calling the FlexDict obj's underlying member method code with example usage: obj.assertSpace(space) without return types